It's going to depend on a lot of factors as to why those AR's failed. After all, yours didn't. If you want to get your knowledge on regarding the AR-15 (M16/M4, etc) then read the M16/M4 Handbook by Mike Pannone. First printing was around 2008.

Per the book:

Originally Posted by M16/M4 Handbook

The key to keeping this system running reliably, with minimum maintenance, is ensuring that all the critical parts related to extraction and ejection and prone to wear are serviceable and relatively clean. These parts are extractor and spring, ejector and spring, gas rings, and buffer spring.

For those of us who have been in the military, this section is quite interesting:

Originally Posted by M16/M4 Handbook

Lubrication.

The M16/M4 system needs to be lubricated properly in order to function reliably. There are only a few points to lubricate, and they are quite pronounced: any point that shows metal-on-metal wear, i.e., bolt lugs, cam pin, and rails on bolt carrier, as well as the previously mentioned point in the trigger group. For years troops were told to keep the bolt "wet" and that the gun would run find. This is true but has a down side. The areas that do not need lubrication, but are dripping with it, will attract dust and debris in a desert environment. With a wet gun, when the first round is fired, it will blow the excess oil out of the gun - usually into your face. Put lubrication where it is needed in reasonable quantities, and the rifle will run just as reliably as a soaking-wet gun. All said, a slightly wetter gun is better than a drier gun, but don't go to the extreme, or you will wind up with an oil-based "mud" in your gun. You should be mindful of the requirements of your rifle in different field conditions (Al Anbar open desert vs. downtown Baghdad).

How many times have we or our NCO's ensured that our/their weapons were "wet".

In any event, the AR is a bit of a precision weapon system with tighter tolerances then a lot of other systems, specifically, the AK. As such, you do have to keep on top of things more so to ensure continued and consistent reliability. Me, I'm a fan of the AR platform, just not so much of a fan of its gas system. But YMMV...